1. Field of the Invention
This invention relates generally to an all-optical Code Division Multiple Access (CDMA) system and, more particularly, to a methodology and a concomitant system for the optical synchronization of the transmitter and receiver in the CDMA system.
2. Description of the Background Art
Optical synchronization will undoubtedly play a central role in helping to introduce all-optical CDMA networks for future bursty and packet-based communications systems. As the speed of all-optical packet communications increases dramatically, the success of optical synchronization will rest upon introducing a very efficient technique in order to obtain the synchronization with minimal required time.
The majority of published works on all-optical CDMA systems assumes perfect synchronization between each receiver and transmitter pair. However, the article entitled “Performance Analysis in Synchronization and System on CDMA Optical Fiber Networks, by G. C. Yang, as published in IEICE Trans. Comm., vol. E77B, No. 10, pp. 1238–1248, in October, 1994 did consider a simple synchronization method for non-coherent optical CDMA and highlighted the importance of synchronization by showing the degradation in the performance of the system when the synchronization between receiver and transmitter is not ideal. Later, the article entitled “Performance of a Serial-Search Synchronizer for Fiber-base Optical CDMA Systems in the Presence of Multi-user Interference” by Mustapha et al., as published in Proc. SPIE. Vol. 3899, pp. 297–306, introduced, first, a serial-search synchronizer. Then, most recently, Mustapha et al. in an article entitled “Dual-Threshold Sequential Detection Code Synchronization”, published in the Journal of Lightwave Technology, vol. 18, No. 12, pp. 1742–1748, December 2000, demonstrated a second-type of sequential method for synchronization of an optical orthogonal code (OOC)-CDMA system. Guided by the aforementioned work, the present inventors have considered the performance of simple serial-search algorithm for code acquisition in an optical CDMA system using OOCs and have noted that the mean time required for synchronization is in the order of half code length bits duration. Long code lengths may be used in a typical system that therefore requires a long period for synchronization.
It is clear that the art is devoid of a multiple-shift technique which not only is simple in its structure but it also greatly improves the performance of synchronization process.